It is well-known that to remove plaque from an artery, a balloon on the tip of a catheter may be positioned where the artery is constricted; and thereafter, the balloon is expanded, which breaks the plaque free, reducing the constriction. The problem has been that this weakens the arterial wall where the balloon has been expanded. It is known in the art to provide a tubular stent at that location to reinforce the artery, the stent remaining in the artery when the operation is completed. One of the problems is the proper location of the stent which will remain in the artery. In order to ensure that the proper location is achieved, x-ray technology is utilized which requires the stent be visible with x-rays. The axial location of the stent is important and axial adjustment of advancement or withdrawal is often required. There have been problems in the past with achieving sufficient visibility and of making final axial adjustment. This invention is of an improved stent which is highly "visible" and which can be readily adjusted axially.
Generally speaking, in a cardiovascular intervention, a catheter having an expandable balloon-type tip is inserted into the artery; and the balloon is expanded when in position at a constricted zone. A tubular catheter is then used to advance a stent along the balloon tipped cather to reinforce the expanded zone. In this invention, between the balloon tip and the distal end of the catheter jacketing the balloon tipped catheter, a stent is provided. It is a generally tubular reinforcement member of a coil spring shape which is provided with rollers to facilitate axial adjustment.
In this invention, the coil shaped stent is provided with a diameter slightly greater than the diameter of the distal end of a tubular catheter jacketing the balloon catheter; and the stent is also of a diameter slightly less than the diameter of the expanded balloon. Thus, when the tubular jacketing catheter or push catheter is advanced, it will bear against the proximal end of the stent and force it in a forward axial direction. To adjust the stent, when a degree of withdrawal is required, the balloon, when expanded, bears against the distal stent end to pull it rearwardly when the balloon catheter is withdrawn somewhat.
In operation, generally speaking, the balloon tip catheter is advanced to the site of the plaque and, there, expanded to free the plaque. The stent is then required to be located where the balloon was expanded. In order to do this, a tubular catheter jacketing the balloon catheter is advanced pushing the stent advancing it along the exterior of the balloon tipped catheter. The location of the stent can then be checked to be sure it is in the correct location using x-rays. If advancement is required, the jacketing catheter is advanced which pushes the stent along the balloon tipped catheter to the correct axially location. On the other hand, if the stent must be withdrawn slightly, the balloon tip is expanded and the balloon tipped catheter is withdrawn slightly pulling the stent axially rearwardly to the correct location. There the stent remains in situ to reinforce the arterial wall. When the stent is properly located, the balloon is collapsed and withdrawn through the stent and removed together with the jacketing tubular catheter.
It is an object of this invention to provide an improved stent which is in the shape of a coil spring of a uniform diameter, formed from a wire along which there are spaced bearings with a roller between adjacent bearings. The spring and rollers are preferably of a suitable metallic material, such as gold or stainless steel.